Localized injections of various compounds effecting neurotransmitter activity in the mammillary complex enhance...

The mammillary complex is implicated in the amnesic syndrome associated clinically with Korsakoff's syndrome, Alzheimer's disease and experimentally with lesions in animals. There is however no direct evidence that the mammillary bodies are involved in long term memory processing. Mice were partially trained on a footshock avoidance task. Immediately after training drugs were injected into the mammillary complex. Retention was tested 1 week later by continuing training until each mouse made five avoidance responses in six trials. The results indicated that muscarine, nicotine, dopamine, glutamine and adrenoceptor agonists as well as GABA and 5-HT receptor antagonists and neuropeptide Y improved retention test performance relative to the control. Injection of the same drugs 1 mm above the injection site for the mammillary complex failed to significantly improve retention test performance. It is concluded that the mammillary complex, with its important connections to other areas of the limbic system, is involved in memory processing events that occur shortly after training.